The present invention relates to a retainer for retaining electronic modules in a holder, and more particularly to a retainer for retaining printed circuit cards in a heat-exchanging cold plate.
The operation of printed circuit cards or other type electronic modules creates heat, which needs to be removed through a heat exchange with some form of heat sink. Often the heat sink used is a special plate, called a cold plate, which contains slots for holding individual printed circuit cards. The printed circuit cards are retained in the slots by a retainer, which is generally a thermal conductive metal block that is fastened along the printed circuit card to create a secondary thermal path. The retainer, along with the printed circuit card, is then placed into the slot of the cold plate.
As shown in FIG. 1a, the prior art retainer, manufactured by the assignee of this patent application, was made of at least four components: a specially manufactured screw 2, a front wedge 4, a body 6a, and a rear wedge 8. Each of these components had ramped ends. In addition, front wedge 4 and body 6a contained lengthwise slots so that they could be slid onto and be retained by screw 2. To further increase the length of this prior art card retainer, additional bodies could be added. In that case, a longer screw was required to be manufactured to accommodate the additional length.
In assembling the prior art retainer, body 6a was first mounted to the circuit card. Screw 2 was then slid through the slots of both front wedge 4 and the mounted body 6. At that point, other bodies could be slid onto screw 2. The additional bodies, however, were not mounted to the circuit card. Finally, rear wedge 8, which had a threaded slot that mated with the threads of screw 2, was threaded onto screw 2 to retain the various components.
The assembled retainer and circuit card unit was then slid into one of the slots of a cold plate. Rear wedge 8 was then tightened to press front wedge 4 and body 6a against the head of screw 2. As a result, ramped body 6a became offset, thereby causing the retainer to press against the sides of the slot.
In order to use the retainer and circuit card unit in another cold plate, rear wedge 8 had to be loosened to release the retainer's pressure against the slot walls. If rear wedge 8, however, was loosened too much, the various components could freely rotate about screw 2. For example, as shown in FIG. 1b, body 6b, a typical unmounted body, could rotate out of alignment with respect to the ramped ends of front wedge 4, body 6a (not shown) and rear wedge 8. As a result, before placing the assembled unit into the new cold plate slot, the various components had to be properly realigned with respect to their ramped ends. This process of realignment was both time consuming and costly.
As indicated, several disadvantages arose from using the prior art retainer. The screw had to be specially manufactured for the particular length of retainer that was desired. The retainer's various components tended to rotate around the screw, thereby making the alignment of the components difficult. In addition, since the screw was not fastened to the card, e.g., it was free-floating, the screw would tend to vibrate, occasionally at resonant frequency. As a result of such vibration, the metal screw would easily fatigue and quickly wear out. Additionally, the vibration would cause the rear wedge to loosen and occasionally unscrew itself off the screw.
An additional disadvantage of the prior art retainer was that it was not in continuous contact with either the circuit card or cold plate slot, since only one body was mounted to the card and the other bodies were offset. As a result of the discontinuous contact between the retainer and the circuit card or cold plate slot, the surface area for conducting both heat and pressure was reduced.
One objective of the present invention is to provide a retainer whose components are not easily misaligned. Another objective is to provide a retainer that supplies a better thermal path to a heat sink. More generally, the objective of the present invention is to provide an improved retainer that is able to overcome the above-mentioned disadvantages.